In article ,
Brian Whatcott wrote:

On Fri, 24 Jun 2005 20:05:29 GMT, Bruce in Alaska
wrote:

In article , Jeff
wrote:

Note that magnetron life (which is a finite resource) is not used up
by standby time.

Actually, the above is not an accurate conclusion. Magnitrons are
a special type of Vacum (sp) Tube, that use a Filiment Anode, that
is Pusled at High Voltage, to create the RF energy that makes the
Transmitter Pulses. There are specific operational time limits
on filiment life for Pulsed and nonPulsed situations. Operating a
magnitron, with just the filiments lite does degrade the life of that
filiment, and will cause it to fail. It just doen't happen as fast as
when the unit is being Pulsed with High Voltage Pulses. Operational Life
is in the range of 1000 to 2000 hours and of that time, most figure 20%
will be in Standby Mode (filiment lite/no HV Pulses). Increasing
the Standby Time will extend Operational Life, but definitly not
forever, and as the filiment ages, MultiPulse, and Frequency Drift will
become issues.


Bruce in alaska

The bit that's pulsed in the magnetron is the cathode at the centrer
of the gadget.
The anode surrounds it, and is the machined copper piece with the
cavities.

But Bruce has it mostly right, I reckon

Brian Whatcott

Well I hadn't had my coffe yet, yesterday and the BrainPan wasn't
operating up to speed yet.....You are correct......


Bruce in alaska
--
add a 2 before @

In article , Jeff
wrote:

It certainly should be - but how do you get it at the correct angle?
We've all seen powerboats with the bow sticking way up. And, if the
powerboat slows, as it should in the fog, then the radar is pointing
down. Clearly, if the bow goes up more than 25 degrees at speed,
there is no way to have the radar work at both high and low speed.

Certainly many powerboats will be using trimtabs to stay reasonably
close to proper trim, but I'm not sure we can say "most" have their
radar at a proper angle. And of course, when that sport fisherman is
blasting down Buzzard's Bay in pea soup at 30 knots, is he really
looking at the radar?

Paul Schilter wrote:
Jeff,
On most power boats the radar is angled down so when the boat is
underway on plane the radar is now level.
Paul


Jeff wrote:

The beam width of small radars is +-12.5 degrees. Thus, if you're
heeling 15 degrees (assuming no leveling device) you're seeing almost
nothing to windward or leeward. If you're bouncing that much, your
signal is intermittent. And if you're a powerboat at speed with the
bow raised 15 degrees, you could be blind in front!

Actually most XBand Radar antennas are designed for 25 degree Vertical
Beamwidths at the 3db Powerpoints, which means your have 12.5 +/-
degrees of level. If you vessel has a Pitch Angle, of more than 12.5
Degrees, your radar mounting is the least of your problems, especially
for a Powerboat.

Me